1. Field of the Invention
The present invention relates to a liquid crystal display device mounted in a portable game device or a mobile phone or a liquid crystal display device used in a display of a personal computer and the like or a liquid crystal television screen and particularly to a liquid crystal display device having a good visibility and a good assembling operability.
2. Description of the Related Art
In a liquid crystal display device mounted in a portable game device or a mobile phone and a liquid crystal display device used in a display of a personal computer and the like or a liquid crystal television screen, the front surface of a liquid crystal display panel is normally covered by a transparent protection plate in order to protect the liquid crystal display panel. Normally, a clearance is defined between the liquid crystal display panel and the transparent protection plate. This is intended to prevent a reduction in display quality caused by local exertion of a pressure on the liquid crystal display panel from a pen at the time of hand-writing input using, for example, an input pen or the like or to protect the liquid crystal display panel from an external shock.
However, since such a clearance leads to formation of an air layer between the liquid crystal display panel and the transparent protection plate, reflection losses of light at these interfaces are large, thereby causing a problem of reduced visibility of the display panel. In order to prevent a reduction in visibility, an attempt has been made to eliminate the air layer by providing a transparent element in a space between the liquid crystal display panel and the transparent protection plate.
For example, Japanese Unexamined Patent Publication No. 6-337411 discloses a method according to which a liquid raw material of a light-confusion preventing member is injected between a liquid crystal display panel and a transparent protection plate and cured to form a shock-absorbing layer (silicone gel, polyurethane elastomer), and placing and adhering the liquid crystal display panel on and to the formed shock-absorbing layer in a reduced-pressure atmosphere.
However, since operations of pouring and curing the liquid raw material have to be carried out in individual apparatuses, productivity is poor. Thus, a technique of providing an already-cured plate-shaped sheet between the liquid crystal display panel and the transparent protection plate has been studied.
For example, Japanese Unexamined Patent Publication No. 6-75210 proposes a method according to which an adhesive sheet made of a transparent tacky resin (acrylic polymer, tacky silicone polymer containing an organopolysiloxane skeleton as a base) and having a shock-absorbing property is provided between a liquid crystal display panel and a transparent protection plate. In such a case, the panel, the plate and the sheet are adhered while being closely attached to each other with a volatile solvent provided on adhesive interfaces, thereby preventing air from getting trapped.
Further, Japanese Unexamined Patent Publication No. 9-133912 discloses a transparent nongelatinous resin (e.g. nongelatinous acrylic polymer) sheet having a shock-absorbing property and tackiness. Here, after a separator on one surface of a resin sheet is peeled off and this surface is adhered to a liquid crystal display panel (or transparent protection plate) by a roll laminator or the like, a separator on the other surface is peeled off and this surface is adhered to the transparent protection plate (or liquid crystal display panel) by a press-adhering method or the like. In the case that air bubbles are trapped at the adhesive interfaces, deaeration is applied using an autoclave or a vacuum deaerator.
Japanese Unexamined Patent Publication No. 9-197387 proposes provision of a transparent resin sheet made of a polymer containing a plasticizer and having a weak adhesiveness. This adhesive resin sheet is placed on the display panel or the transparent protection plate while preparing a volatile liquid to such a degree as not to swell or dissolve, and adhered thereto by a roll laminator or the like. Thereafter, the volatile liquid is supplied and the transparent protection plate or the display panel is placed and adhered by a press-adhering method or the like.
In any of the above methods, the tacky sheet is used and can be placed on the display panel by, e.g. pressing and can be adhered to the transparent protection plate using its tackiness. Thus, these methods have a better productivity than the method according to which the liquid is injected and cured. However, in order to eliminate air bubbles having entered between the interfaces of the sheet and the liquid crystal display panel or the transparent protection plate, the entered air is deaerated by applying the volatile liquid to the interfaces and using the volatility of the applied liquid or by using a reduced-pressure or vacuum deaerator. Such deaeration is, of course, problematic in respect of productivity.
On the other hand, Japanese Unexamined Patent Publication No. 9-6256 proposes a method according to which a transparent tacky sheet made of a polymer whose glass transition temperature is xe2x88x9230xc2x0 C. or lower and having a shock-absorbing property (e.g. acrylic polymer, tacky silicone polymer having an organopolysiloxane skeleton) is provided between a liquid crystal display panel and a transparent protection plate. Such a transparent tacky sheet is excellent in respect of productivity since it can be adhered to the liquid crystal display panel and the transparent protection plate upon being lightly pressed due to its tackiness and it does not require any special deaeration such as application of a volatile liquid or a vacuum deaerator. Further, Japanese Unexamined Patent Publication No. 9-318932 discloses a laminated sheet in which an adhesive layer and a shock-absorbing layer are placed one over the other. This laminated sheet serves to maintain an adhered state and to prevent generation of air bubbles since the shock-absorbing layer thereof can prevent a distortion caused by a pressure given from a pen or the like and the tacky layer thereof can be easily adhered to the liquid crystal display panel or the transparent protection plate without trapping air bubbles at the interface.
However, since the tacky or adhesive sheet is used as a finished sheet in any of the methods using the above finished sheet, there is a problem that the tacky surfaces of the finished sheets are likely to be stained in the case that a liquid crystal display device is assembled while preparing a large number of finished sheets. If the tacky surface is stained, it leads to reduced tackiness. In addition, air enters due to dust or the like adhered to the tacky surface, with the result that reflection loss of light occurs at that portion, thereby reducing a visibility.
If dust or the like should be attached to the tacky surface, there is no means for removing the dust or the like from the tacky surface. Thus, the finished sheet has to be disposed of. On the other hand, at a production site, devices are often assembled using finished sheets having dust or the like attached thereto without noticing the adhesion of dust or the like. This causes a variation in the quality of final products and a poor yield.
An object of the present invention is to provide a liquid crystal display device having a high visibility and a good yield by eliminating trapping of an air layer or air by a simple operation.
An inventive liquid crystal display device comprises a liquid crystal display panel; a nontacky silicone sheet having rubber elasticity and placed on and adhered to the liquid crystal display panel; and a transparent protection plate placed on and adhered to the silicone sheet.
An inventive method for producing a liquid crystal display device comprises the steps of placing a nontacky silicone sheet having rubber elasticity on a liquid crystal display panel; and removing air present at interfaces of the liquid crystal display panel and the silicone sheet by placing the silicone sheet.